mm: add new 'read_cache_page_gfp()' helper function

It's a simplified 'read_cache_page()' which takes a page allocation
flag, so that different paths can control how aggressive the memory
allocations are that populate a address space.

In particular, the intel GPU object mapping code wants to be able to do
a certain amount of own internal memory management by automatically
shrinking the address space when memory starts getting tight.  This
allows it to dynamically use different memory allocation policies on a
per-allocation basis, rather than depend on the (static) address space
gfp policy.

The actual new function is a one-liner, but re-organizing the helper
functions to the point where you can do this with a single line of code
is what most of the patch is all about.

Tested-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index ed5d7501e181..3c62ed408492 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -253,6 +253,8 @@ extern struct page * read_cache_page_async(struct address_space *mapping,
 extern struct page * read_cache_page(struct address_space *mapping,
                                 pgoff_t index, filler_t *filler,
                                 void *data);
+extern struct page * read_cache_page_gfp(struct address_space *mapping,
+                                pgoff_t index, gfp_t gfp_mask);
 extern int read_cache_pages(struct address_space *mapping,
                 struct list_head *pages, filler_t *filler, void *data);